Each error will have an associated HTTP status code. If it is client side errors, then 4XX level status codes willl be returned. If an error occurred on the server side, then 5XX status codes will be returned. The most common status codes that are used for errors are:

We have sought full documentation of errors, and we recognise that this is not yet available, but in the meantime, we have a problem with error handling.

We performed two SendMessage API calls, with one failing and one successful, but on both occasions the messages arrived. We¿d like to know what was going on so we can better handle such exceptions. On the first message send failure, we tried again, but as mentioned, this resulted in two successful messages being sent. It¿s important we design a robust user experience, and so I¿d be very grateful for your assistance.